The present invention provides a railway car coupler or connector with a buff/draft gear assembly. More particularly, the invention relates to a slackless drawbar connector with an integral assembly to cushion the dynamic loading of the slackless connector in the buff and draft directions of the coupled railcars.
The rail industry developed with the steam locomotive, which is a lower torque drive means than the modern diesel locomotive. The steam locomotive did not have the torque capacity to initiate drive on the full length of a train of tightly coupled cars, therefore, a degree of free-travel or free-play between-cars was required to allow sequential initiation of car travel of loaded trains. The coupling apparatus between the cars had to accommodate the longitudinal travel in both directions, and also handled the vertical and horizontal travel at the coupling as the train progressed along the rails. In addition, couplers are generally assembled from as-cast components, which do not have the dimensional tolerances associated with machined elements. Therefore, all the free play and relatively loose connections associated with earlier couplers were acceptable conditions, and as noted above, they were necessary conditions.
The diesel locomotive brought changes in the load-bearing capacity of trains, their physical parameters and their operating characteristics. The physical and mechanical properties of the couplers joining the individual cars of the train also changed to accommodate the train improvements. The greater loads carried by modern railway trains have changed the perception of the coupler engineer and designer with regard to train operating characteristics. Indicative of this change in perception is that heavier loads are carried on rail cars and the industry has moved to maintain close-butted relationships between coupler draft components to lessen the impact forces on cars, couplers and lading.
Since most coupler drawbar connection parts are as-cast pieces with little or no finish machining to provide dimensional control, it is desirable to provide a self-adjusting coupling device to accommodate component wear and to lessen the slack in the coupler connections. One type of self-adjusting articulated coupler is shown in U.S. Pat. No. 3,716,146.
In an exemplary slackless drawbar coupling structure, the drawbar extends between the car sill sides and nests in a pocket casting. The butt end of the drawbar may be convexly arcuate and abut a complementary front concave surface of a follower block. The back surface of the follower abuts the front surface of a wedge, which has a rear surface abutting the rear wall of the pocket casting within the car sill. Either or both of the front and rear surfaces of the wedge member diverge upwardly to yield a gravity-assisted wedging force, which provides the slackless coupling arrangement. When the abutting surfaces become worn, the wedge member drops slightly to maintain the essentially slackless connection.
The top, bottom and vertically disposed side walls in the pocket casting of the drawbar coupling arrangement provide a cavity for the follower and the wedge. Upon horizontal angling of the drawbar, the side walls limit the lateral translation and, therefore, the rotation of the follower about the vertical axis of the arcuate butt end of the drawbar. Rotation of the follower may potentially cause the wedge to rotate about the car longitudinal axis and possibly hang up between the vertical walls, especially when the wedge is small in height relative to its width. A method of controlling rotation of the follower, and the relative orientation with the wedge, provides for a very close tolerance between the vertical side walls of the cavity and the follower side edges. As these are cast components, the procedure providing close tolerances between components requires an uneconomical amount of tolerance design and machining of finished parts.
The term slackless means that the drawbar, or coupler, is received within the center sill in a manner to minimize longitudinal play or movement. As successive railway cars in a train must accommodate relative movement between cars when curves and inclines are negotiated, there must be a provision for each car to move in pitch, yaw and roll modes with respect to the coupler member. Moreover, there must also be a provision to remove the draft components for repair and replacement of parts and, to disconnect coupled cars.
In a slackless system, the coupler member is held in a manner to eliminate, or minimize, longitudinal movement with respect to the car body. As noted above, this may be done by providing a tapered wedge between a rear wall of a pocket casting secured in the center sill and a follower block, which rests against the butt end of the coupler member shank. The wedge tends to force the follower block away from the pocket casting end wall and firmly against the butt end of the coupler member shank. In railway cars being pushed, the longitudinal forces cause compression of the coupler member against the follower, wedge and pocket end wall of the slackless arrangement.
When railcars are being pulled, a draft key or connecting pin acts against the longitudinal forces tending to separate the drawbar from the pocket casting. The pin or draft key is a metal bar extending laterally or vertically through the center sill and a slot or pin bore in the shank of the coupler member. In a slackless drawbar system, the drawbar is held tightly against the connecting pin or draft key by the action of the wedge separating the pocket casting from the follower block. The wedge compresses the follower block against the butt end of the drawbar, which biases the drawbar at the pin bore or slot against the pin or key. However, the mating faces of the follower block and drawbar are preferably curved to allow the drawbar to pivot, both vertically and laterally, and to permit the car to roll with respect to the drawbar. The drawbar may also pivot at the draft key or pin connection on an arcuate pin or key bearing-block interposed between the parts.
In U.S. Pat. No. 4,593,827 to Altherr, a slackless coupler is shown with the drawbar extending into the car center sill. The front surface of a follower block in the center sill has an arcuate concave section abutting the convex arcuate end of the drawbar. The follower block rear surface has a convex shape of two generally planar surfaces joined at a vertex substantially in the vertical center plane of the railcar. The wedge shim is provided with a generally concave surface, which complementarily abuts the convex surface of the follower block. The interrelationship of the shim and block surfaces maintains the orientation of the assembly and inhibits lateral translation between the shim, the follower and the side casting.
U.S. Pat. No. 4,700,853 to Altherr et al. also provides a slackless coupler with the placement of contoured spacer means within the center sill on either side of the coupler member, both above and below the draft key slots, to prevent lateral movement of the drawbar on the draft key. A preferred embodiment also includes access means or ports in the pocket casting for engagement or withdrawal of the wedge from contact with the follower blocks.
Draft gear assemblies have been known and utilized for coupler systems in the prior art, however, they frequently utilized large spring assemblies, which added to the weight of the undercarriage assembly and detracted from the freight carrying capacity of the railway car. Illustrative examples of draft gear assemblies operable to absorb buff and draft forces applied to the draft gear are shown in CAR AND LOCOMOTIVE CYCLOPEDIA, CENTENNIAL EDITION (1974), at page S9-S32. Force diagrams, which illustrate the effect of impact forces on a cushioning device from both directions along the longitudinal axis of the assembly, are noted in some of the figures. The intent of most known draft gear assemblies is generally to protect the freight car structure. Lading protection, however, requires varying degrees of energy dissipation. Sliding sill arrangements to accommodate lading protection are generally complicated assemblies with attendant higher assembly costs. Therefore, end-of-car cushioning devices evolved, which units could be installed outboard of the car bolsters but they do not fit within the standard draft gear pockets. These cushioning units have both greater travel and greater energy absorbing ability than conventional draft gears. The American Association of Railroads, A.A.R., specifications for Special Cushioning Devices for Freight Cars are delineated at A.A.R. specification number M-921-65, and include impact testing, as well as appraisal under actual service conditions and service experience.
Buff gears or buff gear assemblies are also known and utilized in railroad car couplers to form a compression spring assembly. These buff or draft gear assemblies are typically used between railway cars to buffer the impact of adjacent cars, and to compensate for the impact loads on the car couplers during operation of the train. A buff gear arrangement is illustrated in U.S. Pat. No. 4,556,678 to D. G. Anderson and includes a mounting assembly for positioning the cushioning apparatus in the coupler assembly. The buffer operates to absorb the force load from the impact between adjacent cars in a freight train, which impacts may occur during humping of freight cars. However, the utilization of these buff-draft gear assemblies has not been feasible with slackless couplers, as these couplers had to be operable in both the draft and buff directions with little or no longitudinal free play in the coupler assembly.
The present invention provides a shock-absorbing, dynamically-loaded, buff/draft gear apparatus to absorb the load on a slackless railroad car coupler in both the buff and draft directions of travel. The buff/draft gear structure avoids the shock-loading of the coupler assembly from sudden acceleration in the draft direction and retains the shock-absorbing capability of the assembly in the buff direction, especially for freight cars being humped. This buff/draft gear apparatus is operable with slackfree couplers, which are not the articulated type of connectors, without dramatic changes in the center sill or other mechanical structure of the coupler and drawbar assemblies. The buff/draft gear structure is not prohibitively large, which minimizes its space requirements, and it is also adaptable to existing railroad car center sills with draft gear assemblies. The buff/draft gear structure makes the utilization of extant slackless subassemblies adaptable for incorporation into the shock-absorbing apparatus, and provides a variable load-absorbing apparatus for each particular railroad car and coupler, which load-absorbing apparatus is based upon design criteria. This latter variation in shock-absorbing capacity is accommodated by the addition of more or fewer of the axially arranged friction pads in the load-absorbing elements.
The slackless coupler and the buff/draft gear assembly have individually been provided in couplers. However, slackless couplers have less free travel to accommodate the draft-direction coupler loading. Short-travel shock-loads in the draft direction can generate knuckle or coupler wear and damage in a slackless coupler. This concern is alleviated by the present invention as the load is transferred from the connecting pin and pocket-casting to front-stops and eventually to the sidewalls of the side sill. The pocket-casting and front-stops also permit the buff/draft gear to absorb the compressive load in the buff direction over a cushioned-load range and thereafter, the additional buff loading is accommodated through the front stops, and the side sill.